A known type of multi-layer headbox comprises a slice having a slice chamber and a slice opening, a turbulence generator defining a turbulence channel group for supplying stocks to the slice chamber, and at least one separator vane separating two stock channels in order to keep stocks on each side of the separator vane separated from each other when the stocks flow through the slice chamber. The separator vane is detachably mounted at its upstream end directly or indirectly on the turbulence channel group. The detachable mounting of the separator vane is effected by a plurality of short engagement dowels arranged in a row and spaced from each other, extending perpendicularly through the separator vane and protruding from at least one side of the separator vane. The protruding portion of an engagement dowel forms a free engagement end portion. An elongate construction element with a longitudinally extending groove open at both ends is provided for receipt of the upstream end portion of the separator vane and its engagement dowels to secure the separator vane in the machine direction. The groove has at least one longitudinally extending recess that forms support and guide walls facing the free engagement end portions of the engagement dowels.
When a separator vane of the type described above is being manufactured, its end portion, which is located upstream, is provided with a plurality of through-holes located a predetermined distance from the upstream edge of the separator vane. The holes are placed in a row as straight as possible, with equal spacing between them, within a predetermined tolerance interval in relation to a line parallel with the adjacent narrow edge of the separator vane. The aforementioned construction element is manufactured as straight as possible within a predetermined tolerance interval. The groove formed in the construction element is also made as straight as possible from end to end within a predetermined tolerance interval. In certain cases these tolerances at one and the same point along the upstream end portion of the separator vane, the opposing construction element and along the opposing groove, may be added together so that difficulties occur when the upstream end portion of the separator vane and its engagement dowels are inserted into the groove in the construction element from one open end to the other open end. In particular, one or more of the engagement dowels, as a result of the cumulative tolerances, can interfere with one of the support and guide walls inside the groove. One or more of the other engagement dowels may also press against the other support and guide wall in the groove as a result of the tolerances at these points being added together in the opposite direction within the prescribed tolerance interval. Errors caused by difficulties in maintaining prescribed tolerance intervals naturally also result in the above problems.
U.S. Pat. No. 5,545,294 shows a multi-layer headbox having rigid separator vanes, each of which has an upstream end clamped in bundle of tubes of the transverse distributor, and is provided with vane extensions thinner than the separator vanes. The vane extensions are detachably mounted on the separator vanes by means of short engagement dowels in the vane extensions and grooves in the separator vanes.
A jointed connection strip for a separator vane is shown in U.S. Pat. No. 4,133,715, but the separator vane is not provided with engagement dowels and the connection strip is thus not provided with a groove to fit engagement dowels. The object of the present invention is to provide a multi-layer headbox in which each separator vane is mounted in a grooved construction element in such a manner that the forces acting between the engagement dowels and the support and guide walls in the groove of the construction element are greatly reduced.